The invention is based on a pressure fluid reservoir having a dividing piston and a non-contact means for indicating at least one position of the dividing piston. A pressure fluid reservoir is known from German Offenlegungsschrift No. 11 88 247, the dividing piston of which apparatus controls two electrical contact switches, disposed one behind the other outside its cylinder in a longitudinal direction thereof, in a non-contacting manner. By way of example, such switches have magnetically actuatable switching contacts fused into glass tubes, which are known as Reed contacts and are available in commerce. One switch serves to switch on a reservoir charging apparatus and the other switch switches it off, whenever the isolating piston has attained a predetermined position. The shutoff ends a rise in pressure within the pressure fluid reservoir. Depending on the temperature of the pressure fluid reservoir, variably high pressures prevail therein after the shutoff. This pressure difference may be disadvantageously great, especially if the temperature of the pressure fluid reservoir fluctuates between -40.degree. C. and +120.degree. C., for example, as a result of the installation of the pressure fluid reservoir in a motor vehicle, where for example it may be part of a vehicle braking system. The above temperature range accordingly means there will be considerable errors in pressure indications.